1. Field of the Invention
The present invention relates to a reference clock generator used in an optical data recording/reproducing system.
2. Description of the Prior Art
Identification information of the original optical recording medium can be recorded in the burst cutting area (BCA) of the optical recording medium, and the identification information is called the BCA data. The identification information in the BCA of the optical recording medium can be decoded to identify whether the optical recording medium is an original edition or not. The accessing apparatus of the optical recording medium can access the analog RF signal of the BCA, and the BCA data decoder then decodes the BCA data by the analog RF signal of the BCA. This process is called BCA data decoding.
Referring to FIG. 1 and FIG. 2, FIG. 1 is a schematic diagram of the BCA 11 of the optical recording medium of the prior art, and FIG. 2 is a block diagram of the BCA data decoder 13 of the prior art. The BCA 11 is located in an inner part of a lead-in area of the optical recording medium 10. The identifying information of the BCA 11 can be decoded by a BCA data decoder 13 of the prior art.
The BCA data decoder 13 comprises a reference frequency generating circuit 12 and a BCA data decoding circuit 15. The reference frequency generating circuit 12 comprises a quartz oscillator 16 and a frequency divider circuit 18. The quartz oscillator 16 can generate an oscillating frequency. The reference frequency generating circuit 12 is used for generating a BCA reference frequency 14, wherein the BCA reference frequency 14 is obtained according to the oscillating frequency, which is generated by the quartz oscillator 16, and passing the frequency divider circuit 18.
The BCA data decoding circuit 15 comprises a data slicer 22 and a data extractor 32. The data slicer 22 receives the analog RF signal 20 with RF modulation and parallel marks with low reflection rate from the BCA and generates a BCA digital pulse signal 26. Then, the data extractor 32 counts the width of the BCA digital pulse signal 26 by utilizing the BCA reference frequency 14. Finally, the BCA data decoding circuit obtains the identifying information according to the counting result, and the phase encoding principle of the BCA digital pulse signal, the RZ (return-to-zero) modulation method and the data structure of the specification. In the prior art, the spindle motor of the accessing apparatus of the optical recording medium accesses the analog RF signal 20 of the BCA of the optical recording medium 10 in the CAV (constant angular velocity) and counts the BCA digital pulse signal 26 in a constant BCA reference frequency. Because the BCA data decoder 13 of the prior art counts the BCA digital pulse signal 26 by a constant BCA reference frequency 14, the spindle motor needs to process the digital pulse signal with the normalization to obtain the correct decoding information when the CAV rotational speed control of the spindle motor has an error or controls different rotational speed.
In the above prior art, the analog RF signal 20 of the BCA of the optical recording medium 10 is accessed in the CAV; the decoding process not only has an added processing step of normalization of the BCA digital pulse signal 26, but it also can not correctly decode the identifying information because the spindle motor is a machine, and the time of reaching the steady state of the spindle motor is longer than the time of reaching the steady state of the circuit, so the generated BCA reference frequency variation can not synchronize with the RF signal variation of the BCA.